This invention relates in general to rotary cutters for printing presses. More specifically it relates to a rotary cutter that reliably removes trim pieces at a high speed and provides an extremely accurate and simple system for adjusting the location of the cutting blades, both radially and circumferentially.
In rotary printing presses used to manufacture booklets, magazines, labels and a wide variety of other products, a web of paper travels at a high speed through a series of stations that each perform an operation such as printing, perforating, folding or cutting the web. The cutting operations are typically carried out by an opposed pair of cylinders. One cylinder carries one or more knife blades to repeatedly cut the web at some regular spacing along the web as the cylinder rotates. The other cylinder can be solid or segmented, that is, with abutment surfaces for the knife blade or blades carried as assemblies on a core cylinder.
A particularly important application is a double "bleed" cutter where a pair of closely spaced blades cut the web to produce a narrow trim piece. It is important to remove the trim piece from the cutting area, carry it to a collection point away from the cutting zone, and remove it from the cutter at the collection point. The trim control must be reliable, even at high speeds, to prevent stray trim pieces from jamming or otherwise interfering with the product delivery process.
Over the years a number of systems have been developed to produce a rotary cut while at the same time controlling the movement of trim pieces. U.S. Pat. No. 3,857,314 and U.S. Pat. No. 4,073,485 assigned to Gregg Engineering Corp. describe a system for cutting and performing other operations. The '314 patent describes a rotary cutter where a knife is carried in a holder which in turn is mounted on the outer cylindrical surface of a roller.
Trim control in the Gregg System is accomplished by a set of pins mounted on an anvil roller opposed to the roller carrying the knife or knives. The trim pieces are speared on the ends of the pins as they are cut. Rotation of the anvil roller carries them to a stationary comb that strips the trim pieces off the pins. This general system is described in U.S. Pat. No. 3,893,359. U.S. Pat. Nos. 909,957, 1,784,487, 2,095,631 and 4,224,821 describe other mechanical ejection systems for use with rotary cutters.
These trim control systems have many serious problems. First, in any system using pins to impale the trim pieces the pins must extend through the trim piece into a mating hole or recess in order to securely grip the trim. This arrangement means that the abutting cylinder cannot be a smooth, solid surface. In the '359 patent, for example, the pins are located on the anvil cylinder to use the space between the knife blades and the core cylinder as this vertical recess. This arrangement results in a more complex assembly and one which has a significantly longer "set up" time than other systems. This is because in setting the knife blades and pins for a given production run, the operator must locate very accurately and secure both the knife blades and the pin assemblies. This set up involves both circumferential and radial adjustments in position. Another problem with any pin system is destruction of the pins when there is a paper jam. This requires that the entire printing operation be shut down while the pins are replaced. Still another problem with the Gregg system is that the comb that removes trim pieces must act against and be flush with a solid surface underneath the trim piece. In practice, it has proven difficult to remove trim reliably at high speeds using this "scraping" action.
Another more recent cutter and trim control arrangement is described in U.S. Pat. No. 4,143,568 assigned to Butler Automatic, Inc. This system focuses on a solution to a serious defect in the Gregg, Uniweb and other known systems, namely, the vibrations set up in the machine by a solid knife blade rapidly and repeatedly impacting against an anvil surface. A major disadvantage of these vibrations is that they alter the spacing between the knife blades and their associated anvil surfaces resulting in an inferior cut. The Butler solution is to spring mount the knife blades. Trim pieces (the "bleed cut") are impaled on a set of pins held in an elongated "strap" secured between the knife blades. A bar with angled over edge portions reciprocates in coordination with the rotation of the cutter to eject the trim from the pins at a point removed from the cut. As in the Gregg system, since the cylinder size is fixed by the size of the rotary printing press, variations in the length of the cut are made by changing the circumferential location of the knife blade assemblies and opposing anvil surfaces. While locating the pins between the blades provides enhanced protection, the pins nevertheless are subject to destruction during paper jams, they require an opposing hole or recess, and they must be set and adjusted to the proper height to avoid impacting a solid surface while impaling a trim piece to a sufficient depth to hold it securely.
All of the aforementioned systems attempt to meet a variety of important design objectives such as producing a clean cut at high speed, varying the location of the cut, controlling machine vibrations, avoiding blade wear, and reliably removing, transporting and then ejecting trim pieces produced by bleed cuts. The cut location is meticulously set at the beginning of each production run. A major disadvantage of the known systems is that setting the blade height and circumferential location are time consuming tasks that require a high degree of skill. Another significant problem is that after operation, frictional heat generated by the bearing causes expansion of components of the cutter which usually requires a shutdown and re-setting. Each setting and re-setting can last for a portion of an hour to several hours. This lost production time seriously limits the production capability of the entire printing press. Another problem encountered with the solid, fixed mount blades is that after an extended shutdown, during the night, for example, the blades' settings established during operation must be reset. Operation without re-setting results in the blades pounding the anvil surfaces which rapidly dulls the knife blades and sets up severe vibrations in the cutter. A particular problem with double knife blade assemblies for bleed cuts is that adjustments in the height setting of one blade can alter the setting of the other blade. Heretofore, no known rotary cutting system has reliably met all of these design objectives.
It is therefore a principal object of the present invention to provide a rotary cutting system for a printer that makes high quality cuts and reliably controls the retention and ejection of trim pieces at a high speed.
Another object is to provide a cutting system with the foregoing advantages that utilizes a single assembly acting in cooperation with a solid anvil cylinder to achieve both the cutting and the trim control operations.
Another object is to provide a cutting system that is easily, accurately and reliably adjusted with respect to both the height and the circumferential location of the knife blades.
A further object is to provide a cutting system that is characterized by a low vibration level and low level of knife blade wear.
A still further object of this invention is to control the trim pieces without the use of pins or complicated mechanical arrangements.
Yet another object of this invention is to provide a cutting system that provides a wide selection of types and locations of cuts while at the same time having a high degree of commonality of parts for the differing cuts.
A still further object of the invention is to provide a cutting system that is rugged, reliable and utilizes component parts that are comparatively simple to machine.